The liver is the major organ responsible for regulating
and responding to your body's metabolic demands. Your liver must be
functioning well to maintain normal metabolism of carbohydrates,
fats, and protein; it is also responsible for processing and using
several vitamins. This section deals with the role and healthy
liver (and a healthy, well-balanced diet) plays in these
nutritional processes.

Carbohydrate Metabolism

The most common sources of dietary carbohydrate are sugars, such
as sucrose (table sugar), fructose (corn syrup), and lactose (milk
sugar), and starches, such as breads, pasta, grains, cereals,
fruits, vegetables, and potatoes. When you eat carbohydrates,
specialized enzymes in the pancreas and gut process them to yield
simple sugars (glucose, galactose, fructose, maltose).

These sugars are absorbed by intestinal lining cells, enter the
portal circulation, and travel to the liver via the portal vein.
During overnight fasting, blood sugar levels dip to a relatively
low level, insulin secretion is suppressed, and blood insulin
levels diminish. After a meal, blood sugar increases (stimulating
the release of insulin from the pancreas), and insulin levels rise.
Insulin, which rises in response to a meal, is the hormone that
stimulates the liver to take in more glucose and to move the
glucose into storage -- mainly in the form of glycogen. The liver
can then release glycogen to your muscles for energy during periods
of fasting or exercise. Although the liver can store considerable
amounts of glycogen, it is the first energy source used during
periods of prolonged fasting or caloric deprivation, and it can be
depleted rapidly. After glycogen, the body taps other energy
sources -- including protein and fat.

Protein Metabolism

We take in dietary protein from dairy products, produce, and
meats. Enzymes produced by the pancreas and intestine break down
the protein into its amino acids and small peptides. The intestine
rapidly absorbs the amino acids with specific transport systems
within its lining cells and then delivers the amino acids to the
liver via the portal vein.

When they reach the liver, they are used for energy or for
making (synthesizing) new proteins. The newly synthesized proteins
perform specific body functions.

Fat Metabolism

In general, fats are neutral lipids (triglycerides), acidic
lipids (fatty acids), and sterols (cholesterol, plant sterols).
Triglycerides (dairy products, meats, oils, butter, margerine) are
the most common type of dietary fat and represent a major source of
energy. The liver is uniquely suited to regulate and process
triglycerides.

Dietary triglyceride is digested in the intestine by lipase, an
enzyme secreted by the pancreas in response to meals. Bile,
secreted by the liver, makes the digested fat soluble and promotes
its absorption. Absorbed fat is then repackaged and transported
into blood, where the liver ultimately removes it from the
circulation. Fat that reaches the liver is processed in three ways:
(1) stored as fat droplets in liver cells, (2) metabolized as a
source of energy, and (3) repackaged, secreted back into blood, and
delivered to other cells in the body.

The liver is also intimately involved with the processing of
dietary cholesterol and is the main source of newly synthesized
cholesterol in the body. Liver disease may be associated with both
high or low blood cholesterol levels. In general, as liver disease
progresses in patients with hepatitis C, the blood level of
cholesterol drops.

Bile

The liver produces and secretes a fluid (bile) that enters the
intestine to aid in digestion and absorption. Bile is clear yellow
to golden-brown and contains water, electrolytes (salts),
cholesterol, bile salts (detergents), phospholipids, and proteins.
Bile helps to activate enzymes secreted by the pancreas and is
essential for the digestion and absorption of fat or fat-soluble
vitamins.

Vitamins

The liver plays a role in several steps of vitamin metabolism...
Vitamins are either fat-soluble (Vitamins A, D, E, and K) or
water-soluble (Vitamin C and the B-complex vitamins).

Patients with advanced liver disease may become deficient in
water-soluble vitamins, but this is usually due to inadequate
nutrition and poor food intake. Vitamin B12 storage usually far
exceeds the body's requirements; deficiencies rarely occur due to
liver disease or liver failure. When dietary intake drops, however,
thiamine and folate commonly become deficient. Oral supplementation
is usually all that you need to restore thiamine and folate stores
to the normal range.

Fat-soluble vitamins require not only adequate dietary intake
but also good digestion and absorption by the body. That's why
normal production of bile is essential. Bile in the gut is required
for the absorption of fat-soluble vitamins into the body because
these vitamins are relatively insoluble in water. Bile acts as a
detergent, breaking down and dissolving these vitamins so they may
be properly absorbed.

If bile production is poor, oral supplementation of vitamins A,
D, E, and K may not be sufficient to restore vitamin levels to
normal. The use of a detergent-like solution of liquid vitamin E
(TPGS) improves the absorption of vitamin E in patients with
advanced liver disease. The same solution may also improve the
absorption of vitamins A, D, and K if the latter are taken
simultaneously with the liquid vitamin E.